A vehicle braking system for use on a wheeled vehicle generally includes a rotating device that rotates with a wheel while the vehicle is in motion and a second device that is mounted to an apparatus on the vehicle body itself and that does not rotate with the wheel while the vehicle is in motion. When the brakes are applied, the apparatus moves the second device into contact with a surface or surfaces on the rotating device to create friction between the rotating device and the friction device. The resulting friction causes the speed of the vehicle to decrease. In a vehicle with a disk braking system, the rotating device is commonly referred to as a brake disk or a brake rotor while the second device is commonly referred to as a brake pad. In a vehicle with drum brakes, the rotating device is commonly referred to as a drum while the second device is commonly referred to as a brake shoe. The terms “brake rotor” and “brake pad” are used throughout this disclosure to refer generically and respectively to a rotating device of a braking system and a second device of a braking system.
A braking system can include one or more components operable to move a friction material or other surface on the brake pad to forcibly contact with a friction surface of the brake rotor. The braking system can be controlled by a user operable mechanism, such as a foot-operated brake pedal or a hand-operated grip device and can be mechanical, electrical, hydraulic, or the like. For braking systems featuring a brake rotor, the mechanism can be a set of calipers and a mechanical, electrical, hydraulic, etc. system for applying pressure to one or more brake pads mounted to each caliper to urge it/them against the friction surfaces of the brake rotor. The brake rotor typically has two opposing friction surfaces on opposite annular faces of a disk-like structure, which can optionally include vanes or other internal structures for providing ventilation, reducing weight, or otherwise supporting some amount of non-solid volume disposed between the two opposing friction surfaces, etc. In brake drum systems, the friction surface of the drum is typically on the inner rotation surface. The brake shoes are urged against the friction surface by calipers, levers, pistons, or other devices that are controlled by the user.
Brake rotors are generally made of a durable material while brake pads are made of a material that wears away under the friction resulting from stopping or slowing a vehicle. However, brake rotors typically also experience wear and eventually require replacement or re-machining, which can be expensive. Additionally, particulate debris from brake pads generated during braking are typically released to the environment. Because of the chemical compositions typically employed in brake pads, this particulate debris can include constituents, including but not limited to copper, cadmium, lead, mercury, and the like, that are known or suspected to have harmful effects when found in significant quantities in the environment. In addition, the heat generated during the braking process can promote reactions between chemical components of the brake pad, which can cause the formation of toxic materials and/or gases.
Currently available brake rotors are most frequently manufactured out of cast iron for a number of reasons. For example, one or more physical properties of cast iron, such as for example the ability to handle large amounts of heat generated during braking and the relative ease with which it can be cast and formed into a necessary shape, can be desirable. In addition, cast iron is generally quite inexpensive as a bulk material (in particular in comparison to other materials such as stainless steel, titanium, carbon fiber, and the like that are used in some braking applications). Production processes for cast iron brake rotors are also relatively established and well-known. Furthermore cast iron is generally accepted as a standard brake rotor material.
However, cast iron is relatively soft. It works well as a brake rotor due to its interactions with a brake pad, which can generate significant friction. Cast iron tends to wear due to this friction interaction, and as it does so it introduces particulate matter to the environment. Particulate materials are strongly suspected of causing health issues and other environmental problems. Furthermore, rotor wear requires regular and costly maintenance of a braking system of a vehicle, typically including re-machining or even replacing the brake rotors on a regular basis.